The present invention relates to rotors for vehicle dynamos.
A conventional rotor of a vehicle dynamo is shown in FIG. 4. The rotor consists of a rotary shaft 3; a pair of field cores 1 and 2 secured to the rotary shaft 3 such that pole claws 1a and 2a each extending inwardly from the free end thereof alternately mesh each other to form an annular channel; a bobbin 4 mounted in the annular channel; and a field coil 5 placed in the bobbin 4.
When rotation is transmitted to the rotary shaft 3 via a driving pulley (not shown) to rotate the rotor, with a field current supplied to the field coil 5 by a current collector (not shown), power is generated in a fixed coil (not shown) mounted around the rotor. The field coil 5 of the conventional dynamo suffers from high temperatures arising from the heat generation or reception. When the field coil is at high temperatures, the electrical resistance becomes high, making the field current and the magnetomotive force lower. As a result, the output current of the vehicle dynamo is lower than the output current at cold conditions as shown in FIG. 5. The output current in a high-temperature atmosphere is also lower than the output current in a normal-temperature atmosphere as shown in FIG. 6.